PREFACE TO THE SECOND EDITION. 



WHEN the First Edition of this work was published, I sup- 

 posed that the general theory set forth in its Second Part, 

 was presented in something like a finished form; but sub- 

 sequent thought led me to further developments of much 

 importance, and disclosed the fact that the component 

 parts of the theory had been wrongly put together. 

 Even in the absence of a more special reason, I had decided 

 that, on the completion of the Principles of Biology j& would 

 be proper to suspend for a few months the series I am 

 issuing, that I might make the required re-organization. 

 And when the time had arrived, there had arisen a more 

 special reason, which forbade hesitation. Translations into 

 the French and Kussian languages were about to be made 

 had, in fact, been commenced ; and had I deferred the re- 

 organization the work would have been reproduced with 

 all its original imperfections. This will be a sufficient ex- 

 planation to those who have complained of the delay in the 

 issue of the Principles of Psychology. 



The First Part remains almost untouched : two verbal 

 alterations only, on pp. 43 and 99, having been made to 

 prevent misconceptions. Part II., however, is wholly trans- 

 formed. Its first chapter, on " Laws in General," is omitted, 

 with a view to the inclusion of it in one of the latter volumes 

 of the series. Two minor chapters disappear. Most of the 

 rest are transposed, in groups or singly. And there are nine 



new chapters embodying the further developments, and 



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